Date: Thu, 7 Jan 1999 18:24:23 -0500 (EST) From: "John S. Dyson" <dyson@iquest.net> To: dillon@apollo.backplane.com (Matthew Dillon) Cc: tlambert@primenet.com, dyson@iquest.net, pfgiffun@bachue.usc.unal.edu.co, freebsd-hackers@FreeBSD.ORG Subject: Re: questions/problems with vm_fault() in Stable Message-ID: <199901072324.SAA01200@y.dyson.net> In-Reply-To: <199901072306.PAA35328@apollo.backplane.com> from Matthew Dillon at "Jan 7, 99 03:06:21 pm"
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Matthew Dillon said: > > Huh? Where's the cache? What? No cache? Are you nuts? Or are you > assuming the client-side caches the object locally. But then, where's > the cache coherency? Right out the window. > .... > > There ISN'T only one object. I will repeat that a thousand times. > Your entire model assumes that there is only one object or that all the > VFS layers can be collapsed. Neither assumption works. > Those ARE the key points. The cool thing (and I am agreeing with you Matt) is that the VM method is an abstraction that fully supports the file I/O model also. The file I/O method doesn't support an mmap model at all (at least in a coherent way.) Rather than spending lots of time trying to make a (conventional) VFS scheme work, and adding lots of hacks to simulate coherency, we can start with a hybrid Heidemann/VM framework with proper invalidation protocols and have everything work from the beginning!!! I don't think that any of us are suggesting that the Heidemann framework be ignored. We are suggesting that it should be applied in a different way that gives us alot more flexibility and consistancy. This would allow the infrastructure to do more of the work (almost automatically supporting coherency) rather than adding hackery to a filesystem scheme to force VM mmap coherency. This scheme that Matt and I propose would simplify and truely define the interfaces. -- John | Never try to teach a pig to sing, dyson@iquest.net | it makes one look stupid jdyson@nc.com | and it irritates the pig. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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